Apparatus for laser cutting a workpiece

ABSTRACT

An apparatus is disclosed for cutting a workpiece. A laser beam is directed at successive points along a workpiece surface to be cut and a sensor emits a sensing beam directed at the same successive points as the cutting beam. A beam combining device receives both the sensor beam and the cutting beam and causes downstream beam segments to be collinear with each other as they impinge the workpiece surface. The cutting is thereby able to be carried out in a single pass, and is precise, repeatable and independent of cutting depth, angle of cutting, scoring patterns, material inconsistency, material color, and surface grain variability.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of U.S. Ser. No. 09/811,152,filed Mar. 16, 2001.

BACKGROUND OF THE INVENTION

[0002] This invention concerns apparatus for cutting workpieces by alaser beam to remove material by vaporization. In such apparatus, thelaser beam is advanced along points forming a predetermined cuttingpattern on a workpiece surface.

[0003] A widely used method for determining the extent of materialremoved during controlled cutting involves the use of triangulation typesensors as described in U.S. Pat. No. 5,883,356. These sensors, however,due to their triangulation operating principle, are limited in theirability to reach the bottom of the scoring produced by the cuttingdevice. This is particularly so for narrow, deep penetrations which maybe produced by cutting devices such as lasers and cutting knives.Furthermore, due to their offset mounting, these sensors are not wellsuited to measure the varying penetration depth that occurs duringscoring at a specific location. This is especially true if the scoringpenetration is in the form of partial perforations or slots. As such,the process does not lend itself to scoring the workpiece in an adaptivecontrol mode, where both depth sensing and cutting are in registry witheach other to impinge the same point on the workpiece, during theprogression of scoring of the piece.

[0004] Accordingly it is an object of this invention to provide anapparatus for laser beam cutting in a manner that provides accurateadaptive process control, single-pass processing, and lowermanufacturing costs.

SUMMARY OF THE INVENTION

[0005] According to the invention, the cutting of the workpiece isaccomplished by apparatus including a source of a controllable cuttinglaser beam, which, based on feedback obtained from at least one sensoremitting a sensing beam, is controlled in intensity together withcontrolled relative movement between the laser and the workpiece,producing a precise, predetermined cutting penetration into theworkpiece along a predetermined pattern.

[0006] In this apparatus, the laser cutting beam and sensing beamemitted from a first sensor are both directed at a surface on one sideof the workpiece. A second sensor may also be positioned on the oppositeside of the piece emitting a second sensor beam in opposition to thecutting laser beam. A beam combining device combines the laser cuttingbeam and first sensor beam together so as to have collinear segmentsdirected at exactly the same point on the workpiece. The cutting of theworkpiece is carried out by the laser beam while the piece is moved in apredetermined pattern relative to the laser. The depth of cutting of thework piece by the laser beam is controlled by real time feedback signalscorresponding to the depth of the cut provided by the first sensor. Todetermine material thickness remaining during cutting of each pointalong the predetermined pattern, real time feedback from the secondsensor can be provided combined with the feedback signals from the firstsensor. The sensor feedback can also be utilized to control the movementof the workpiece relative to the laser beam to enhance the cuttingprocess control.

[0007] This apparatus, due to the collinear arrangement of the impingingsegments of the sensor and cutting beams, affords several advantages,including single-pass adaptive processing, cutting precision, andsuperior piece-to-piece repeatability. The cutting achieved is alsoindependent of cutting depth, angle of cutting, scoring patterns,material inconsistency, material color, and surface variations.

[0008] Relative motion between the workpiece and the cutting beam to cutthe piece in a predetermined pattern can be provided by different meansincluding actuators, robots and X-Y tables.

[0009] The workpiece can have a monolayer, multilayer, or compositeconstruction and can be scored on either side. The cutting can becontinuous, intermittent or be a combination of both, and extendcompletely through one or more layers of the piece. The piece can be afinished part or a component which is subsequently integrated into afinished part.

DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a diagrammatic view of one form of the apparatusaccording to the invention including two sensors

[0011]FIGS. 2, 2A and 2B are fragmentary enlarged views of severalalternative designs of the beam combining device incorporated in theapparatus shown in FIG. 1.

[0012]FIG. 3 is a perspective view of an automotive instrument panelwith an integrated airbag deployment door formed by in a U patternscoring carried out by the apparatus of the present invention.

[0013]FIGS. 4 through 6 are cross sectional views of sample monolayerand multilayer trim piece constructions on which various types of trimpiece weakening scorings can be made by the present apparatus.

[0014]FIG. 7 is a diagrammatic view of a second embodiment of theapparatus according to the invention incorporating only a single sensor.

[0015]FIG. 8 is a diagrammatic view of another form of second embodimentof the apparatus according to the invention incorporating only a singlesensor.

DETAILED DESCRIPTION

[0016] In the following detailed description, certain specificterminology will be employed for the sake of clarity and particularembodiments described, but it is to be understood that the same is notintended to be limiting and should not be so construed inasmuch as theinvention is capable of taking many forms and variations within thescope of the appended claims.

[0017] This invention describes an improved apparatus for cutting aworkpiece with a laser cutting beam.

[0018]FIG. 1 shows a first embodiment of a workpiece cutting apparatus10 according to the invention. This includes a laser cutting beam source12 which generates a laser cutting beam which can be used to carry outcontrolled scoring of a surface 14 on one side of a workpiece such as aninstrument panel trim piece 16 that would overlie an airbag installationwhen installed.

[0019] The trim piece 16 is positioned on a holder which can comprise afixture 18. A first sensor 20 is provided to determine the depth ofscoring produced by the laser cutting beam B impinging onto the surface14 of the trim piece 16 to score the same. The first sensor 20 and thelaser cutting beam generator 12 are connected to a beam combining device22. The beam combining device 22 (shown in detail in FIG. 2) is designedto combine the separately generated electromagnetic sensing beam Aemanating from the first sensor 20 and the laser cutting beam B fromsource 12 so as to be in a collinear relationship and to direct thecombined segments of the sensor beam A and cutting beam B so as toimpinge the same precise spot on the trim piece surface 14. This beamcombining device 22 will also redirect any reflected beam or beamsrequired for sensor operation from the trim piece surface 14 back to thefirst sensor 20 as necessary in carrying out the process.

[0020] The trim piece 16 is moved relative to the cutting laser beamsource 12, as well as the first sensor 20 and the beam combining device22 via a motion actuator 24 drivingly engaged with the holder comprisedof fixture 18 to cause tracing of a particular scoring pattern on thesurface 14 and to achieve a precisely controlled rate of scoring. Themotion actuator 24 can itself directly hold and move the trim piece 16itself or move the optional fixture 18 onto which the trim piece 16 ismounted. Alternatively, the motion actuator 24 could be used to move thelaser beam source 12 and the first sensor 20 relative to the trim piece16.

[0021] A second sensor 26 may be located on the side of the trim piece16 opposite the first sensor 20, a second sensor beam emanatingtherefrom, directed at the outer surface 28 of the trim piece 16 andaligned opposite the same trim piece point as is the laser cutting beamand the first sensor beam or beams are directed in order to control thescoring so as to produce a programmed thickness of material remainingafter scoring. This is done by combining signals generated by bothsensors 20, 26 to create a feedback signal corresponding to thethickness of the remaining material.

[0022] The apparatus 10 is operated via one or more industrialcontrollers 30 that control the scoring effected by the laser and/or themovement of the motion actuator based on a particular program andfeedback signals provided by the sensor 20, 26.

[0023] Lasers that in particularly desirable for carrying out this typeof scoring processes are of the carbon dioxide, excimer, solid state,argon gas, or diode type. However, based on the workpiece materialsutilized (polymers, fabrics, wood, leather), the carbon dioxide laser islikely to be the most preferable in terms of operability, efficiency andcost. The laser can be operated either continuously or in a pulsed mode.

[0024] Different type of sensors can be utilized to measure the extentof material removed or remaining during scoring of the trim piece. Forthe first sensor 20, connected to the beam combining device 22, apreferred type is a closed loop device that sends and receives aspecific beam of electromagnetic radiation in order to determine thedepth of scoring effected by the laser. The Conoprobe sensors offered byOptimet and based on the technique of conoscopic holography, is one suchsensor commercially available. In this type of sensor, an emitted laserbeam and reflected return beams of visible light have segments alsotraveling in a collinear relationship with each other and the laserbeam. Another type of sensor that could be utilized is one that detectsreflected light beams such as a high speed CCD camera. In thisapplication, the reflected beam will be reflected from the trim piecesurface being scored by the cutting beam.

[0025] For the second sensor 26 aimed at the outside surface of the trimpiece, which is generally smooth and accessible, there are more numerousoptions than electromagnetic beams and including infrared, laser,ultrasonic, conoscopic, CCD camera, proximity and contact type sensors.

[0026] The signal spot size of the first sensor beam selected can varysignificantly. Generally the smaller the spot size the better. For thefirst sensor, the preferred size would not exceed the size of thescoring produced on the trim piece by the cutting laser beam. For thesecond sensor, if surface finish variations, so called grain, aresignificant, its spot size should preferably not exceed 300 microns.

[0027] There are numerous ways for combining the separately originatedcutting laser beam B and sensor beam A to create collinear segmentsthereof. FIG. 2 shows the inner details of the beam combining device 22which combines the separate laser beam B and the first sensor beam A tocreate collinear segments which impinge the trim piece surface 14. Thebeam combining device 22 includes a reflector 32 having coatings causingreflection of light of the wavelength of the sensor beam A from itsinclined surface while allowing the cutting laser beam B to betransmitted.

[0028] Such coated selective reflectors are commercially available. Thisof course requires that the laser and sensor beams be of differentwavelengths.

[0029] A side entrance tube 29 directed at the reflector 32 is connectedto the first sensor 20. The main tube 31 mounts the reflector 32, maintube 31 having an end opening 33 directed at the trim piece 16.

[0030] The segment of the sensor beam A reflected from the reflector 32is caused to be collinear, i.e., aligned and coextensive with thesegment of the laser beam B past the reflector 32, with both collinearsegments then impinging the surface 14 at the same precise point.

[0031]FIG. 2A shows a second form of a beam combining device 22A havingan inclined reflector 32A having coatings causing reflection of a beamhaving the wavelength of the cutting laser beam B, while allowingtransmission of the beam having wavelengths of the sensor beam A to betransmitted therethrough to reverse the relationship shown in FIG. 2.

[0032]FIG. 2B is a simplified diagrammatic view of another form of thebeam combining device 22B combining the cutting laser beam B and thefirst sensor beam A to produce collinear downstream segments thereof.This embodiment includes a simple mirror reflector 36 having a throughhole 34. The hole 34 is small in diameter relative to the diameter ofthe cutting laser beam B in order to minimize or eliminate the effectthat the presence of the hole 34 may have on reflecting the cuttinglaser beam from the mirror reflector 36 to redirect the cutting laserbeam B. Such a mirror does not require coatings that arewavelength-selective such as those shown in FIGS. 2 and 2A in order tocombine segments of the beams into a collinear relationship. In thisparticular arrangement, the first sensor 20 could be a CCD camerareceiving beams reflected from the trim piece surface being scored bythe laser beam.

[0033] In order to apply the complete scoring pattern, the trimworkpiece is preferably moved relative to the laser beam and/or thesensors. The relative motion can be applied by a various types of motionactuators including robots and X-Y tables. During cutting, the sensorthickness data can also be used to control the movement of the motiondevice in order to apply the scoring along the predetermined pattern.The workpiece may be held directly by the motion device or be attachedto a holding fixture held by the motion device. The holding fixture maybe shaped to match the shape of the workpiece and/or be designed toregister specific surface features of the workpiece. Vacuum or clampscould also be applied to the holding fixture to hold the trim piecesurface in better contact with the fixture 18. The fixture 18 can bedesigned to allow the second sensor 26 to have physical and/or opticalaccess to the surface 28 of the workpiece (i.e., transparent fixturewall, opening in fixture wall, etc.).

[0034] The process controller 30 is designed to control the operation ofthe laser and/or motion actuator based on the feedback signals providedby the two sensors 20, 26 which, from opposites sides or surfaces of thetrim piece 16, monitor the location being scored. The two sensors 20, 26working in tandem determine the remaining thickness of the trim piece 16at any point they are directed to. During laser scoring at a givenpoint, the two sensors 20, 26 provide signals from which a measurementof the material thickness remaining after the scoring can be derived bythe control device 30. Based on this real-time thickness determination,the process control device 30 controls the operation of the cutting beamsource 12 to effect only the desired extent of material removal intendedfor any given point on the workpiece 16. The remaining thickness datacan also be used to control the motion actuator 24 to move the workpiece16 to the next desired location along the predetermined scoring pattern.

[0035] Due to the collinearity of the impinging segments of the firstsensor beam and the cutting beam, several advantages are realized thatcould not be attained by any of the existing processes. Since the firstsensor beam and the laser beam are always impinging on the same point onthe trim piece, the process becomes insensitive to a large number of keyvariables, including the angle of cutting, the depth of the penetration,the trim piece thickness, the configuration of the weakening patternand, to a large extent, the speed of cutting. Also, the combination ofthe two sensors provides for a direct remaining thickness measurement,superior scoring precision and excellent part to part repeatability. Inaddition, the process enables the user to overcome variations in trimpiece thickness, material properties such as density, color, voids andsurface grain. These and other benefits are obtained while operatingwith rapid adaptive control in a single-pass mode.

[0036] This apparatus can be used in various ways, such as to cut orscore a workpiece continuously or to form discontinuous cuts such asslots, grooves, etc., therein.

[0037] A second embodiment of the apparatus 44 according to theinvention is shown in FIG. 7 where the outer surface 42 of the trimpiece 16 is in intimate contact with the inner fixture wall 46. In thisarrangement, the distance between the first sensor 48 and the fixtureinner wall 46, along the predetermined scoring pattern, can be measuredprior to starting the scoring operation. If this distance can bemaintained constant from pass to pass, then the second outside sensorwould not be necessary while still running the process in a single-pass,adaptive control mode.

[0038]FIG. 8 shows another embodiment of the apparatus 50 where thefirst sensor 52 is mounted immediately alongside the cutting beam source12 so that both beams A, B are substantially collinear with each otherto approximate the effect of using the beam combining device 22described.

[0039] The laser cutting beam may also function as the sensor. Thisarrangement also maintains the collinear configuration as the sensingsignals and the laser beam are generated by the same laser. Under thisapproach, the laser beam characteristics and control would bemanipulated to conduct sensing measurements during or between cuttingintervals (i.e., sensing after a preset number of cutting pulses).

1. An apparatus for weakening a workpiece, comprising: a laser sourcefor a cutting beam able to score a surface on one side of saidworkpiece; a holder for holding said workpiece in a position so thatsaid laser cutting beam is directed at said surface of said workpiece; amotion actuator imparting relative motion between said source of saidlaser cutting beam and said workpiece in a predetermined pattern; asensor arrangement for monitoring the remaining material thickness ofsaid workpiece, said sensor arrangement including a first inner sensordirecting a sensing beam towards each point on said workpiece which isbeing scored by said laser cutting beam; said sensor arrangement alsoincluding a second outer sensor detecting an opposite surface of saidworkpiece; a beam combiner combining said laser cutting beam and saidfirst sensor sensing beam in a collinear relationship, said collinearbeams continuously thereby directed at the same point on said workpiece;and, control means responsive to the extent of said scoring of saidworkpiece at each point along said predetermined pattern detected by themonitoring of said first and second sensors to correspondingly adjustthe scoring effect of said cutting beam to produce a predeterminedthickness of said workpiece remaining after said scoring along saidpredetermined pattern.
 2. The apparatus according to claim 1 whereinsaid first sensor beam source is a laser beam source.
 3. The apparatusaccording to claim 1 wherein said first sensor beam is comprised ofelectromagnetic radiation.
 4. The apparatus according to claim 1 whereinsaid holder comprises a fixture shaped to provide intimate contact withsaid opposite surface of said workpiece.
 5. An apparatus for cutting aworkpiece, comprising: a laser source for generating a laser cuttingbeam able to cut into a surface of said workpiece; a holder for holdingsaid workpiece in a position so that said cutting beam is directed at asurface of said workpiece; a motion actuator imparting relative motionbetween said laser cutting beam and said workpiece to create cutting ofsaid workpiece in a predetermined pattern; a sensor arrangement formonitoring the extent of cutting effected on said trim piece by saidcutting beam, said sensor located on the same side of said workpiece assaid generating a sensing beam directed from the same side towards thepoint on said workpiece point being cut by said cutting beam; a combinerdevice combining downstream segments of said laser cutting beam and saidsensing beam to be a collinear with each other, said collinear beamsegments both directed at the same point on said workpiece; and, controlmeans responsive to said monitoring of said cutting on said workpiece ateach point along said predetermined pattern by said sensor arrangementto adjust the cutting effected by said cutting beam in correspondencethereto to produce a predetermined extent of cutting along saidpredetermined pattern.
 6. The apparatus according to claim 5 whereinsaid sensing beam is a laser beam.
 7. The apparatus according to claim 5wherein said sensor beam is comprised of electromagnetic radiation. 8.The apparatus according to claim 5 wherein said workpiece holder is afixture shaped to provide intimate contact with surface of saidworkpiece opposite said surface cut by said cutting beam.
 9. Anapparatus for forming lines of weakening in a workpiece, comprising: alaser cutting beam source producing a laser cutting beam able to score asurface of said workpiece; a holder for positioning said workpiece sothat said laser cutting beam is directed at a surface of said workpiece;a motion actuator imparting relative motion between said laser cuttingbeam source and said workpiece to trace a predetermined pattern on saidsurface; a sensor arrangement monitoring the extent of material removaleffected by said laser cutting beam, said sensor producing a sensingbeam directed towards said surface of said workpiece; and, a beamcombining device receiving both said cutting and sensing beams,combining respective downstream segments of said beams in a collinearrelationship, and directing the combined beam segments at said surfaceof said workpiece.
 10. The apparatus according to claim 9 wherein saidsensing beam is a laser beam.
 11. The apparatus according to claim 9wherein said cutting and sensor beams are electromagnetic radiation ofdifferent wavelengths, and said sensing and cutting beams are bothdirected at a reflector which selectively transmits one beam andreflects the other as a result of their difference in wavelengths tocombine said beams into a collinear relationship with each other. 12.The apparatus according to claim 11 wherein said reflector is inclinedat 45° and said one beam is directed at a front face thereof to bereflected and the other beam is directed at a rear face of saidreflector through which it is transmitted.
 13. The apparatus accordingto claim 10 wherein said sensor beam is of much smaller diameter thansaid cutting beam and wherein said cutting beam is directed at aninclined reflector surface having a hole formed therein of a muchsmaller diameter than said cutting beam, and said sensor beam isdirected through said hole in a direction parallel to said cutting beamafter being reflected from said reflector.